自定义注解实现字段有条件的判空

背景

代码实现

1、新建自动以注解类

package com.atguigu.springcloud.annotation;

import java.lang.annotation.ElementType;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.annotation.Target;

@Target({ElementType.FIELD})
@Retention(RetentionPolicy.RUNTIME)
public @interface ConditionalNotEmpty {

    //错误提示信息
    String message();

    //判断依据的字段名称
    String conditionFiledName() default "";

    //判断条件，如本例中 18
    String contionString() default "";
}

2、新建Student类

package com.atguigu.springcloud.annotation;

import lombok.Data;

@Data
public class Student {
    @ConditionalNotEmpty(message = "name不能为空")
    private String name;
    @ConditionalNotEmpty(message = "age不能为空")
    private String age;
    @ConditionalNotEmpty(message = "sex不能为空",conditionFiledName = "age",contionString = "18")
    private String sex;

    public Student(String name, String age, String sex) {
        this.name = name;
        this.age = age;
        this.sex = sex;
    }

    @Override
    public String toString() {
        return "Student{" +
                "name='" + name + '\'' +
                ", age='" + age + '\'' +
                ", sex='" + sex + '\'' +
                '}';
    }
}

3、新建ConditionalNotEmptyExplain类

package com.atguigu.springcloud.annotation;

import org.apache.commons.lang3.StringUtils;
import java.lang.reflect.Field;

public class ConditionalNotEmptyExplain {
    public static <T> void validate(T t) throws IllegalAccessException, NoSuchFieldException {
        // 获取当前对象所有字段信息
        Field[] declaredFields = t.getClass().getDeclaredFields();
        for (Field field : declaredFields) {
            // 判断字段是否被注解 ConditionalNotEmpty 解释
            if (field.isAnnotationPresent(ConditionalNotEmpty.class)) {
                // 功能是启用或禁用安全检查,设置为true
                field.setAccessible(true);
                // field.get(t)获取当前字段值，如果有值则判断下个字段
                if (field.get(t) != null) {
                    continue;
                }
                // field.get(t)获取当前字段值，如果为空则继续判断是否需要条件判断
                ConditionalNotEmpty annotation = field.getAnnotation(ConditionalNotEmpty.class);
                // 获取message参数值
                String message = annotation.message();
                // 获取conditionFiledName参数值
                String conditionFiledName = annotation.conditionFiledName();
                // 获取contionString参数值
                String contionString = annotation.contionString();
                // 如果conditionFiledName和contionString不为空，则直接打印出message
                if (StringUtils.isNotEmpty(conditionFiledName) && StringUtils.isNotEmpty(contionString)) {
                    // 根据依赖字段conditionFiledName(比如本例字段age)，反射得到这个依赖字段的信息
                    Field conditionFiled = t.getClass().getDeclaredField(conditionFiledName);
                    conditionFiled.setAccessible(true);
                    // 获取当前依赖字段值(比如本例字段age)
                    Object conditionFiledValue = conditionFiled.get(t);
                    // 进行判断如果当前依赖字段值等于注解参数contionString值则满足条件（本例当前字段age值10等于注解参数contionString10，则打印）
                    if (conditionFiledValue != null && contionString.equals(conditionFiledValue)) {
                        if (field.get(t) == null) {
                            System.out.println("当"+conditionFiled.getName()+"为"+conditionFiledValue+"时"+message);
                            continue;
                        }
                    }
                }else {
                    // 如果conditionFiledName和contionString为空，则直接打印出message
                    System.out.println(message);
                }
            }
        }
    }
}

4、测试结果

// 1、当name、age、sex都为空时
public class TestMain {
    public static void main(String[] args) throws IllegalAccessException, NoSuchFieldException {
        Student student = new Student(null,null,null);
        ConditionalNotEmptyExplain.validate(student);
    }
}
控制台打印结果：
name不能为空
age不能为空


// 2、当age、sex为空时
public class TestMain {
    public static void main(String[] args) throws IllegalAccessException, NoSuchFieldException {
        Student student = new Student("zhangsan",null,null);
        ConditionalNotEmptyExplain.validate(student);
    }
}
控制台打印结果：
age不能为空


// 3、当age=18、sex为空时
public class TestMain {
    public static void main(String[] args) throws IllegalAccessException, NoSuchFieldException {
        Student student = new Student("zhangsan","18",null);
        ConditionalNotEmptyExplain.validate(student);
    }
}
控制台打印结果：
当age为18时sex不能为空


// 4、当age=19、sex为空时
public class TestMain {
    public static void main(String[] args) throws IllegalAccessException, NoSuchFieldException {
        Student student = new Student("zhangsan","18",null);
        ConditionalNotEmptyExplain.validate(student);
    }
}

控制台打印结果：
没有打印结果